Moisture-resistant, coated thermoplastic film having enhanced adhesion to inks and metallic layers

ABSTRACT

A two-step, sequential coating method is disclosed which permits the use of aqueous precursor solutions to coat water-insoluble compounds onto thermoplastic film. In a preferred embodiment, an aqueous oleic acid/ammonium oleate solution is coated onto amorphous polyester sheet which is subsequently monoaxially oriented by stretching in the machine direction, and coated with an aqueous solution of calcium hydroxide, thereby forming a layer of calcium oleate in situ. The coated film is subsequently biaxially oriented by stretching in the transverse direction, and heat-set.

This application is a division of 07/116,107 filed Nov. 3, 1987 now U.S.Pat. No. 4,880,695.

BACKGROUND OF THE INVENTION

The present invention relates to the field of oriented thermoplasticfilms having utility in packaging and solar control applications. Moreparticularly, the present invention relates to a coated thermoplasticfilm which is resistant to moisture and which exhibits enhanced adhesionto inks and to metallic coatings deposited onto the film.

Oriented thermoplastic film, particularly biaxially oriented filmcomposed of polyethylene terephthalate (PET), is widely used as apackaging material for a variety of products, including foodstuffs.

Because the surface of oriented PET film is hydrophobic, it is notreadily receptive to coating or printing. In many packaging and labelapplications it is advantageous that the film be receptive to ordinaryflexographic and rotogravure printing inks.

In an attempt to remedy this deficiency, special inks have been devisedthat adhere directly to the surface of PET film. However, many such inksare based on formulations of organic solvents, resinous binders andother ingredients which are costly, difficult to handle and hazardousfor use in the manufacturing plant.

Another approach for improving the printability of PET film is to applya primer coating which adheres to the film and is receptive as well toprinting inks applied thereto. Examples of such primer coatings includepolymeric compositions based on vinylidene chloride terpolymers such asdisclosed in U.S. Pat. No. 2,698,240 or water dispersible copolyesterprimers such as disclosed in U.S. Pat. No. 4,252,885. The problem withthis approach to enhancing ink adhesion to PET film is that the film isin many instances used as a food packaging material and consequently therelative toxicity of the primer layer becomes important. Thoughpolyester film per se is approved as a food packaging material by mostGovernmental agencies, including the U.S. Food and Drug Adminstration,polyester film primed with certain polymeric primer coatings such asacrylics, vinylidene chloride-containing polymers and many other similarprimers raises toxicity problems because of potential migration of saidprimer material into foodstuffs with which it is in contact.

Coated polyester films having superior ink adhesion properties aredisclosed by U.S. Pat. Nos. 4,486,483 and 4,544,200. The non-toxiccoatings disclosed therein comprise alkali metal salts of unsaturatedfatty acids and alkali metal salts of alkyl sulfates.

In many instances thermoplastic film coated with a metal has replacedmetallic foils, such as aluminum foil, for applications such as labelsand decals, solar window film, packaging films, decorative products andmicrofilm. Among other uses, the metallic foils serve to hinder theonset of oxidative rancidity of the products either prepared in orserved with certain edible oils by preventing the passage of visible andultraviolet light. PET, when coated with a thin metallic layer, providessuperior oxygen and moisture barrier properties, along with the visibleand ultraviolet light barrier properties common to metallic foilpackaging applications at a greatly reduced cost. Unfortunately, themetal to film bond can fail in many applications, thereby reducing theperformance of the metallized film. One approach for improving theadhesion of the metal to PET film is to heat the coated film asdisclosed in British Pat. No. 1,370,893. The drawback to this method isthe experimentation which must be performed in order to determine theproper temperature and time elements for this procedure before anymetallized film may be produced. Another appoach has been to coatpolyester film with a layer comprising a random copolymer of ethylenewith from 0.5 to 15 weight percent of a 3 to 6 carbon alpha-mono-olefinas disclosed in European Publication No. 0,023,389. Although PET filmswith this type of coating display a certain improvement in metaladhesion over uncoated PET, they also display an undesirable coatingpattern.

A third approach is to coat the polyester film with a copolyestercoating which enhances the metal adhesion properties of polyester film.U.S. Pat. No. 4,493,872 teaches a specific sulfonated copolyestercoating which provides superior metal adhesive properties to orientedthermoplastic film.

The moisture resistance of the coatings applied to polyester films maybe important in applications where the coated film is placed in arelatively humid or moist environment. For example, polyester filmsemployed in food packaging may be exposed to moisture due tocondensation from refrigeration and/or high humidity and temperaturelevels during microwave cooking of the food contained within thepackaging. Unfortunately, the non-toxic, ink adhesion coatings disclosedin U.S. Pat. No. 4,486,483 do not possess superior resistance tomoisture.

Similarly, it is desirable that metalized film possess resistance tomoisture, especially in solar control applications where condensationcan readily form on the window. Unfortunately, the sulfonatedcopolyester metal adhesive coating disclosed in U.S. Pat. No. 4,493,872does not possess superior resistance to moisture.

SUMMARY OF THE INVENTION

The present invention relates to a moisture-resistant coatedthermoplastic film comprising

(i) an oriented thermoplastic film;

(ii) a moisture-resistant coating on at least one side of said film,said coating having been applied to said film by sequentially coatingsaid film with at least two aqueous solutions, one solution containing aprecursor A and the other solution containing a precursor B, such that Aand B react to form a composition C upon said film which is lesswater-soluble than either A or B.

In one preferred aspect, the present invention is a moisture-resistant,coated polyester film comprising

(i) an oriented polyester film;

(ii) a primer coating on at least one side of said film comprising analkaline earth salt of a fatty acid having from 10 to 18 carbon atoms,

said primer coating being present at a weight effective to improve theadhesion of printing inks to said film.

In another preferred aspect, the present invention is a coated polyesterfilm which exhibits resistance to moisture and which is produced by theprocess comprising

(i) extruding a substantially amorphous polyester resin in sheet-likeform and subsequently cooling said resin to form cast polyester sheet,

(ii) coating said sheet with a first aqueous solution comprising atleast one fatty acid having from 10 to 18 carbon atoms;

(iii) subsequently orienting said polyester sheet in the longitudinaldirection, thereby forming monoaxially oriented polyester film,

(iv) coating said monoaxially oriented polyester film with a secondaqueous solution containing an alkaline earth hydroxide,

(v) subsequently orienting said monoaxially oriented polyester film inthe transverse direction thereby forming biaxially oriented polyesterfilm,

(vi) heatsetting said biaxially oriented polyester film.

In yet another aspect, the present invention is a process for applying awater-insoluble alkaline earth salt of a fatty acid onto a thermoplasticfilm comprising

(i) coating said film with a first aqueous solution comprising at leastone fatty acid having from 10 to 18 carbon atoms;

(ii) subsequently overcoating said aqueous coating with a second aqueoussolution containing a water-soluble alkaline earth compound, therebyforming at least one water-insoluble alkaline earth salt of a fatty acidhaving from 10 to 18 carbon atoms,

(iii) removing the water from the film by evaporation to form awater-insoluble alkaline earth salt primer coating upon the web, saidprimer coating being present at a weight effective to improve theadhesion of printing inks to said film and wherein said film is preparedby melt extruding a substantially amorphous polyester film andthereafter orienting said film by stretching in one or two directionsand heat setting said film, said coatings being applied to said filmprior to stretching in one direction, or subsequent to stretching in onedirection but prior to stretching in a mutually perpendicular direction,or subsequent to stretching but prior to winding the oriented film.

DESCRIPTION OF THE INVENTION

The oriented thermoplastic film which forms a part of the presentinvention may comprise, but is not limited to, polyester, polyamide,polycarbonate, or polyolefin, such as polyethylene and polypropylene.Oriented polyester film is preferred.

The preferred oriented polyester film for the purposes of this inventionis made from polyethylene terephthalate, although the invention isequally applicable to polyester film prepared from the polycondensationof a glycol such as ethylene glycol or butanediol and mixtures thereofwith terephthalic acid or mixtures of terephthalic acid and otherdicarboxylic acids such as isophthalic acid, diphenic acid and sebacicacid, or their polyester forming equivalents, which polyesters are madeby methods well known in the art. The film may be produced byconventional techniques using well known apparatus.

For example, the polyester may be melted and extruded as an amorphoussheet onto a polished revolving casting drum to form a cast sheet ofpolymer. Thereafter, the film may be axially stretched in one direction,either in the direction of extrusion ("machine direction") orperpendicular to the direction of extrusion (transverse) in the case ofmonoaxially oriented film. Biaxially oriented film is stretched in boththe longitudinal and transverse directions. The first stretching step ofthe cast sheet may be in either of these two orthogonal directions. Theamount of stretching employed to impart strength and toughness to thefilm can range from about 3.0 to about 5.0 times the original cast sheetdimension in one or both directions. Preferably, the amount ofstretching is in the range of between about 3.2 and 4.2 times theoriginal dimension. The stretching operations are carried out attemperatures in the range of from about the second order transitiontemperature to below the temperature at which the polymer softens andmelts.

Where desired, the film is heat treated, after stretching, for a periodof time necessary to crystallize the polyester film. Crystallizationimparts stability and good tensile properties to the film. Whenpolyethylene terephthalate is heat treated, it is subjected to atemperature in the range of between about 190° C. and 240° C. and, morepreferably, in the range from about 215° C. and 235° C.

The present invention provides a sequential coating process in which twoaqueous solutions containing water-soluble precursors of the moistureresistant coating composition are sequentially coated on the samesurface of an oriented thermoplastic film. As the second aqueoussolution is overcoated upon the first aqueous solution, thewater-soluble precursors react to form a composition in situ upon thefilm which is less water soluble than either precursor. The processpermits the aqueous coating of a water-insoluble compound upon anoriented thermoplastic film. The advantages of the instant processinclude the avoidance of potentially hazardous volatile organic solventsand the environmental problems associated with such solvents.

One preferred embodiment of the present invention relates to an orientedpolyethylene terephthalate film having a moisture-resistant primercoating applied thereto. The moisture-resistant primer coating comprisesthe alkaline earth salt of a fatty acid having from 10 to 18 carbonatoms, said primer coating being present at a weight effective toimprove the adhesion of printing inks to the polyethylene terephthalatefilm.

Aqueous solutions of fatty acids having from about 10 to 18 carbon atomsare believed useful in the preferred embodiment of the presentinvention. An aqueous solution of oleic acid is preferred. Additionalexamples include aqueous solutions of palmitoleic, ricinoleic andpetroselinic acids.

A small amount of a weak base may be added to the aqueous fatty acidsolution to enhance the solubility of the fatty acid. Ammonium hydroxideis preferred as the weak base. For example, from 3 to 7 weight percentammonium hydroxide may be conveniently added to a 0.025 mole oleic acidaqueous solution.

Aqueous solutions of Group II hydroxides are believed useful in thepreferred embodiment of the present invention. An aqueous solution ofcalcium hydroxide is especially preferred.

The aqueous coating solutions of the present invention may be applied tothe oriented thermoplastic film by any of the well known coatingtechniques employed in the film manufacturing arts. For example, coatingmay be effected by roller coating, spray coating, slot coating orimmersion coating. In a preferred embodiment, the polyester film iscoated by means of gravure roller coating. Also, the polyester filmsurface is preferably subjected to a corona discharge by a coronadischarge apparatus prior to coating as is disclosed in U.S. Pat. Nos.3,520,959; 3,820,929; and 4,028,032. The discharge treatment decreasesthe hydrophobic character of the polyester film surface, which permitsthe water-based coating to more easily wet the surface and thus improvethe adhesion of the coating to the film surface.

The sequential coating process of the present invention may be performedprior to any orientation of the film web ("pre-draw"), between the firstand second orientation stretching steps ("inter-draw"), afterorientation has been completed ("post draw") or a combination ofpre-draw, interdraw and/or post-draw coating procedures may be employed.Pre-draw coating of the film web with the ammonium salt solutionfollowed by interdraw coating with the alkaline earth compound ispreferred.

The quantities of the water-soluble precursors sequentially depositedupon the film surface are dependent upon their coating solutionconcentration and coating application rate. Either stoichiometricamounts of the water-soluble precursors or an excess of either precursormay be deposited onto the film surface.

The preferred concentrations of the water-soluble precursors should beadjusted so as to yield a final dry "composite" coating weight of about1×10⁻⁸ to 2×10⁻⁵ lbs per square foot of film surface. Preferably, thedry "composite" coating weight range is from about 2×10⁻⁷ to 7×10⁻⁶ lbsper square foot, with 8×10⁻⁷ lbs per square foot being the target weightof the moisture resistant coating.

The sequential coating process of the present invention does not requirethat the first coating be dried prior to application of the secondcoating. However, contamination of the second solution by the firstcoating solution may occur if the first coating is not substantially drybefore the second coating is applied. When drying is desired thenecessary heat may often be supplied by appropriate adjustment of theorientation process parameters. Alternatively, forced air, infraredheating or a combination of these methods may be optionally employed todry the coating.

In the preferred embodiment the first coating solution is applied to theforward drawn polyester sheet, and is dried by conventional means beforethe second coating solution is applied. Drying of the second coating isaccomplished during the transverse orientation of the film.

A major application of the moisture-resistant film of the preferredembodiment of this invention is as a packaging or label material. Theprimed polyester films exhibit superior adhesion to aqueous and organicsolvent-based flexographic and rotogravure printing inks in comparisonto unprimed polyester film. The instant films exhibit superior moistureresistance and equivalent ink adhesion when compared to the non-toxicprimer coatings disclosed in U.S. Pat. No. 4,486,483.

Polyester films which have been primed with the alkaline earth saltprimer coating of the present invention also possess excellent utilityas a base for the production of metallized films.

Metallized films can be prepared by forming a coating on a surface ofthe coated polyester film by directing a stream of metal vapor or atomsonto the surface of the film by a vacuum deposition technique. This canbe achieved by heating the metal in a high vacuum, preferably in therange of about 10⁻³ to about 10⁻⁵ torr, to a temperature above itsmelting point such that the vapor pressure of the metal exceeds about10⁻² torr. Alternatively, the metal to be deposited can be subjected toa stream of bombarding ions whereby the metal is removed by masstransfer "sputtering", in which metallic atoms or vapors are emitted inall directions. These vapors or atoms impinge on the film surface,condense and thereby form a thin metallic coating on the film. Masstransfer sputtering coating techniques can be applied to zinc, nickel,silver, copper, gold, indium, tin, stainless steel, chromium, titaniumand, most preferably, aluminum, and include also the oxides of suchmetals. The thickness of the applied metal coating is a matter ofpreference depending upon the final use of the metallized film. Aluminumcoatings in packaging applications may range from about 300 to 600angstroms, while aluminum coatings in solar applications are generallyless than 100 angstroms in thickness.

EXAMPLES

The following Examples illustrate the practice and advantages ofspecific embodiments of the present invention. In no event should thesespecie embodiments of the generic invention be construed as limiting thescope of the claims.

Example I Manufacture of Polyester Film Primed With Calcium Oleate

This Example illustrates that the order of coating the aqueous precursorsolutions onto the film web is not important (assuming, of course, thatthe solubilities of the solutes is not an issue). Two polyester filmsamples were each prepared by sequentially applying the two precursorsolutions without a drying step between the coatings. In the firstsample run, an aqueous solution of oleic acid/ammonium oleate (0.025moles/liter) was coated on the PET film and subsequently overcoated withan aqueous solution of calcium hydroxide (0.025 moles/liter). Thecoating sequence was reversed for the second film sample: calciumhydroxide (0.025 moles/liter) was overcoated with oleic acid/ammoniumoleate (0.025 m/l).

The preparation of these calcium oleate coated films is summarizedbelow:

Polyethylene terephthalate polymer was melted and extruded through aslot die onto a casting drum maintained at a temperature of about 20° C.The melt froze to form a cast polyester sheet. The cast polyester sheetwas longitudinally stretched at a draw ratio of approximately 3.5:1while being maintained at a temperature of about 80° C.

The uniaxially oriented polyester film was then electric coronadischarge treated on both sides of the film at 2.8 watt-min/foot² priorto being sequentially coated as described above.

The coated film was then stretched in the transverse direction at a drawratio of 3.9:1 to produce a biaxially oriented film, which was then heatset at a maximum temperature of 230° C.

The oleic acid/ammonium oleate solution was prepared by adding from 3 to7 weight percent ammonium hydroxide (based on the weight of the oleicacid) to a 0.025 mole aqueous solution of oleic acid.

There was considerable contamination of the coating solution in thesecond coater by the first coating solution, which led to theprecipitation of calcium oleate in the coating roll of the secondcoater.

Example II Evaluation of Ink Adhesion

Samples of the two calcium oleate primer-coated polyester films ofExample I were evaluated for ink adhesion using eight different inksystems. The ink adhesion tests were conducted by applying the inks tocut pieces of the film samples by a draw down technique using a No. 6Meyer rod, followed by oven drying of the ink at 140° F. for a least oneminute. A strip of adhesive tape (Scotch brand No. 610) was adhered tothe dried inked surface, rubbed with the finger to insure intimatecontact, and then rapidly pulled away from the film. The amount of inkremaining in the area which was under the tape is expressed as apercentage of the area, i.e., no ink removed equals 100% adhesion; allink removed equals 0% adhesion, with intermediate adhesion values beingassessed in terms of the proportion of ink remaining adhered to thefilm.

Results of the adhesion tests are compared to an unprimed PET controlfilm in Table I below:

                                      TABLE I                                     __________________________________________________________________________    Ink Adhesion                                                                                      CZ FMB     CONVERTER's MYLEX                                                                          GPI SUNESTER                      Sample                                                                              Green Marker                                                                          Blue Spray                                                                          Red  White/Red                                                                           Blue  White/Blue                                                                           Blue White/Blue                   __________________________________________________________________________    1     98%     100%  96%  96%   99%   98%    99%  97%                          2     98%     100%  96%  98%   99%   97%    100% 99%                          Control A                                                                           99%*          100%*                                                                              100%*              100%*                                                                              100%*                        Control B                                                                           98%*           95%*                                                                               98%*              100%*                                                                              100%*                        __________________________________________________________________________     Legend:                                                                       Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.                Control B is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2500.                *This data was not generated at the time Example I was peformed; rather,      they are data which has been collected at other times but under similar       laboratory conditions.                                                   

Example III - Metal Adhesion

Samples of two calcium oleate coated polyester films produced in ExampleI were evaluated for metal adhesion by placing the samples of theone-side coated film thus produced in a twelve inch laboratory vacuumcoater. The vacuum chamber was evacuated to less than 10⁻⁴ torr pressureand approximately 500 Angstoms of aluminum was evaporated onto thecoated film sample surface from a tungsten filament.

Within 30 minutes after removal from the vacuum chamber, each samplesurface was tested for metal "rub-off" by lightly rubbing the metalsurface with a cotton swab using the same number of rubs andapproximately the same pressure for each sample tested. The samples werefurther evaluated by rubbing a pencil eraser across the surface of thefilm. A third evaluation was performed by laminating an ethylene vinylacetate film to the metallized PET, subsequently delaminating the twofilms, and estimating the amount of metal removed from the PET film as aresult of delamination.

Results of the metal adhesion tests are set forth in Table II below:

                  TABLE II                                                        ______________________________________                                        Metal Adhesion                                                                                                EVA lamination/                               Sample   Cotton Swab Eraser Rub Delamination                                  ______________________________________                                        1        Excellent   Excellent  Excellent                                     2        Good        Excellent  Excellent                                     Control A                                                                              Excellent*             Excellent*                                    Control B                                                                              Excellent*             Good*                                         ______________________________________                                         Legend:                                                                       "Excellent" means that visual observation could not detect that any metal     was removed from the film sample surface.                                     "Good" means that a small amount of metal was visually observed as having     been removed from the film sample surface.                                    "Fair" means that a considerable amount of metal was visually observed as     having been removed from the film sample surface.                             Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.                Control B is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2500.                *This data was not generated at the time Example II was performed; rather     they are data which has been collected at other times but under similar       laboratory conditions.                                                   

Example IV Moisture Resistance

Moisture resistance is evaluated by heat sealing one end of a one inchwide strip of the test film sample to a one inch wide strip of ethylenevinyl acetate film using a Sentinel heat sealer operated at 350° F., 1.5seconds dwell, and 40 psi pressure. The test/EVA strip is thenvertically hung under a 48 gram load in an environmental oven maintainedat 100° F. and 80% relative humidity. The time to heat seal failure isan indication of the resistance to moisture of the test film.

Samples of the two calcium oleate primer-coated polyester films wereevaluated for moisture resistance together with samples of three otherpolyester films. Test results and descriptions of the three other filmsamples are set forth in Table III.

                  TABLE III                                                       ______________________________________                                        Moisture Resistance                                                           Sample       Elapsed Time (seconds)                                           ______________________________________                                        2            399                                                              1            377                                                              Control A    257                                                              Control B    139                                                              ______________________________________                                         Legend:                                                                       Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.                Control B is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2500.           

Example V

Two samples of calcium oleate coated polyester film were producedaccording to the process set forth in Example I, except that theconventional reverse gravure coating of the second coater was modifiedto a "direct" gravure coater in which the coating roll rotated in thedirection of travel of the web instead of against the direction of filmtravel. The alteration of the second coating application did noteliminate the contamination problem experienced in Example I.

Samples of the calcium oleate primed polyester film prepared in ExampleV were evaluated for ink adhesion and metal adhesion. Test results areset forth in Tables IV and V.

                  TABLE IV                                                        ______________________________________                                        Ink Adhesion                                                                                  CZ                                                                    Green   FMB     INMONT 841                                                                              GPI SUNESTER                                Sample  Marker  Red     Blue      Blue                                        ______________________________________                                        3       100%     95%    100%       90%                                        4       100%    100%    100%       90%                                        Control A       100%    100%      100%                                        ______________________________________                                         Legend:                                                                       Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.           

                  TABLE V                                                         ______________________________________                                        Metal Adhesion                                                                                                EVA Lamination/                               Sample   Cotton Swab Eraser Rub Delamination                                  ______________________________________                                        3        good        fair       good                                          4        good        fair       good                                          Control A                                                                              Excellent   Excellent  Excellent                                     Control B                                                                              Excellent   Excellent  Good                                          Control C                                                                              Fair        Fair       Fair                                          ______________________________________                                         Legend:                                                                       "Excellent" means that visual observation could not detect that any metal     was removed from the film sample surface.                                     "Good" means that a small amount of metal was visually observed as having     been removed from the film sample surface.                                    "Fair" means that a considerable amount of metal was visually observed as     having been removed from the film sample surface.                             Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.                Control B is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2500.                Control C is an unprimed polyester film commercially available from           Hoechst Celanese Corporation under the trademark HOSTAPHAN ® 2400.   

Example VI Manufacture of polyester Film Primed With Calcium Oleate

Three samples of calcium oleate coated film were prepared according tothe procedure summarized below. The first film sample was not coronatreated; the second film sample was corona treated on the coated sideonly at a power level of 2.8 watts min/ft² ; and the third film samplewas corona treated on both sides at a power level of 2.8 watt min/ft²per side.

In addition to the three calcium oleate coated films, two control samplefilms were also prepared. Sample VID film was coated only with oleicacid/ammonium oleate, while Sample VIE was coated only with calciumhydroxide.

Polyethylene terephthalate polymer was melted and extruded through aslot die onto a casting drum maintained at a temperature of about 20° C.The melt froze to form a cast polyester sheet. The cast polyester sheetwas longitudinally stretched at a draw ratio of approximately 3.5:1while being maintained at a temperature of about 80° C.

Prior to longitudinal stretching the polyester cast sheet was electriccorona treated as described above and then coated with an aqueous 0.0875mol solution of oleic acid/ammonium oleate.

The coated, longitudinally drawn polyester was subsequently overcoatedwith a 0.025 mol solution of calcium hydroxide. The overcoated film wasdried at a temperature of about 100° C. Thereafter, the film wasstretched in the transverse direction at a draw ratio of 3.9:1 toproduce a biaxially drawn film. The biaxially drawn film was heat set ata maximum temperature of 230° C. The dry weight of the coating was about1.625×10⁻³ lbs per 1,000 square foot of film, with an excess (2.9×10⁻⁴lb/1000 square feet) of calcium hydroxide on the film. The thickness ofthe base PET film was about 0.48 mil.

It should be noted that since the first coating is applied prior to thecast polyester sheet being forward drawn at a ratio of 3.5 to 1, theconcentration of the first coating must be 3.5 times greater than theconcentration of the second coating to obtain an equalconcentration/unit area of finished film assuming the same wet laydown.

Samples of these films were evaluated for metal and ink adhesion byfollowing the procedures set forth above. Tests results are recited inTable VI and VII:

                  TABLE VI                                                        ______________________________________                                        Metal Adhesion                                                                                                EVA Lamination                                Film     Cotton Swab Eraser Rub /Delamination                                 ______________________________________                                        Control B                                                                              Poor        Poor       Good                                          VI (A)   Fair        Poor       Poor                                          VI (B)   Good        Fair       Good                                          VI (C)   Good        Fair       Good                                          VI (D)   Good        Fair       not performed                                 (oleic acid)                                                                  VI (E)   Good        Fair       not performed                                 [Ca(OH).sub.2 ]                                                               ______________________________________                                         Legend:                                                                       Control B is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2500.                "Excellent" means that visual observation could not detect that any metal     was removed from the film sample surface.                                     "Good" means that a small amount of metal was visually observed as having     been removed from the film sample surface.                                    "Fair" means that a considerable amount of metal was visually observed as     having been removed from the film sample surface.                             "Poor" means that all or almost all of the metal was visually observed as     having been removed from the film sample surface.                        

                  TABLE VII                                                       ______________________________________                                        Ink Adhesion                                                                                    GPI        INMONT                                                   GREEN     SUNESTER   841      CZ-FMB                                  FILM    MARKER    BLUE       BLUE     RED                                     ______________________________________                                        Control A                                                                             not       100%       100%     100%                                            performed                                                             VI (A)  100%      100%       100%     100%                                    VI (B)  100%      100%       100%     100%                                    VI (C)  100%      100%       100%     100%                                    VI (D)   30%       0%         95%      70%                                    (oleic acid)                                                                  VI (E)   30%       95%       100%      95%                                    [Ca(OH).sub.2 ]                                                               ______________________________________                                          Legend:                                                                      Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.           

Example VII Pre-Draw/Inter-Draw Sequential Coating Evaluation

Three samples of calcium oleate primed polyester film were preparedaccording to the following procedure:

Polyethylene terephthalate polymer was melted and extruded through aslot die onto a revolving casting drum maintained at a temperature ofabout 20° C. The molten polymer froze to form a cast polyester sheet andwas subsequently coated with an aqueous solution of oleic acid/ammoniumoleate and dried prior to being longitudinally stretched at a draw ratioof approximately 3.5:1 while being maintained at a temperature of about80° C.

The uniaxially oriented, ammonium-oleate-coated film was surface treatedby means of an electric corona discharge prior to being coated with a0.1% by weight aqueous solution of calcium hydroxide. The coated filmwas then dried and stretched in the transverse direction at a draw ratioof approximately 3.9:1 to produce a biaxially-oriented film, which wasthen heat-set at a maximum temperature of about 230° C.

The three polyester films prepared as summarized above differed in theconcentration of the ammonium oleate aqueous solution. The three filmsamples were evaluated for ink adhesion and metal adhesion according tothe experimental procedures recited above. Moisture sensitivity wasevaluated by making a heat seal of the test film to EVA film (using aSentinel sealer, 350° F., 1.5 sec. dwell, 40 psi). The 1" wide strip ishung under tension (48 g) in an environment oven (100° F., 80% RH). Thetime elapsed before the seal failed is recorded. Results are set forthin the following tables:

                  TABLE VIII                                                      ______________________________________                                        Metal Adhesion                                                                                                EVA Lamination                                Sample   Cotton Swab Eraser Rub Delamination                                  ______________________________________                                        VII (A)  Excellent   Excellent  Excellent                                     VII (B)  Excellent   Excellent  Excellent                                     VII (C)  Excellent   Excellent  Excellent                                     Control A                                                                              Excellent   Excellent  Excellent                                     ______________________________________                                         Legend:                                                                       Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.                "Excellent" means that visual observation could not detect that any metal     was removed from the film sample surface.                                     "Good" means that a small amount of metal was visually observed as having     been removed from the film sample surface.                                    "Fair" means that a considerable amount of metal was visually observed as     having been removed from the film sample surface.                        

                  TABLE IX                                                        ______________________________________                                        INK ADHESION                                                                                CZ-FMB   INMONT 841                                             Sample        Red      Blue                                                   ______________________________________                                        VII (A)       60%      100%                                                   VII (B)       60%      100%                                                   VII (C)       50%      100%                                                   Control A     100%     100%                                                   ______________________________________                                         Legend:                                                                       Control A is a primed polyester film commercially available from Hoechst      Celanese Corporation under the trademark HOSTAPHAN ® 2600.           

                  TABLE X                                                         ______________________________________                                        Moisture Resistance                                                           Sample       Elapsed Time (seconds)                                           ______________________________________                                        VII (C)      310                                                              VII (B)      250                                                              VII (A)      230                                                              Control A    170                                                              Control B     70                                                              Control C     45                                                              VII (C)      385                                                              VII (A)      260                                                              Control A    190                                                              VII (B)      180                                                              Control B    115                                                              Control C     65                                                              VII (A)      240                                                              VII (C)      230                                                              VII (B)      200                                                              Control A    180                                                              Control B    150                                                              Control C    130                                                              ______________________________________                                    

We claim:
 1. A process for applying a water-soluble alkaline earth saltof a fatty acid onto a polyester film comprising(i) coating said filmwith a first aqueous solution containing at least one fatty acid havingfrom 10 to 18 carbon atoms; (ii) subsequently overcoating said aqueouscoating with a second aqueous solution containing a water-solublealkaline earth compound, thereby forming a water-insoluble alkalineearth salt of a fatty acid having from 10 to 18 carbon atoms; (iii)removing the water from the film by evaporation to form awater-insoluble alkaline earth salt primer coating upon the web, saidprimer coating being present at a weight effective to improve theadhesion of printing inks to said film and wherein said film is preparedby melt extruding a substantially amorphous polyester film andthereafter orienting said film by stretching in one or two directionsand heat setting said film, said coatings being applied to said filmprior to stretching in one direction, or subsequent to stretching in onedirection but prior to stretching in a mutually perpendicular direction,or subsequent to stretching but prior to winding the oriented film. 2.The process of claim 1 in said first aqueous solution is applied to saidfilm prior to stretching in the longitudinal direction.
 3. The processof claim 2 wherein said second aqueous solution is applied tomonoaxially oriented film prior to stretching said film in thetransverse direction.
 4. The process of claim 3 in said first aqueoussolution comprises oleic acid and said second aqueous solution comprisescalcium hydroxide.
 5. The process of claim 4 in said first aqueoussolution additionally contains from 3 to 7 weight percent of ammoniumhydroxide, based upon the amount of oleic acid present in said solution.6. A process for applying a water-insoluble alkaline earth salt of afatty acid onto a polyester film comprising(i) coating said film with afirst aqueous solution containing a water-soluble alkaline earthcompound, (ii) subsequently overcoating said first aqueous solution witha second aqueous solution comprising a fatty acid having from 10 to 18carbon atoms, thereby forming a water-insoluble alkaline earth salt of afatty acid having from 10 to 18 carbon atoms; (iii) removing the waterfrom the film by evaporation to form a water-insoluble alkaline earthsalt primer coating upon the web, said primer coating being present at aweight effective to improve the adhesion of printing inks to said filmand wherein said film is prepared by melt extruding a substantiallyamorphous polyester film and thereafter orienting said film bystretching in one or two directions and heat setting said film, saidcoatings being applied to said film prior to stretching in onedirection, or subsequent to stretching in one direction but prior tostretching in a mutually perpendicular direction, or subsequent tostretching but prior to winding the oriented film.
 7. The process ofclaim 6 said first aqueous solution is applied to said film prior tostretching in the longitudinal direction.
 8. The process of claim 7wherein said second aqueous solution is applied to monoaxially orientedfilm prior to stretching said film in the transverse direction.